CN108574404B - Duty ratio control circuit and soft start method of bidirectional DCDC converter - Google Patents

Duty ratio control circuit and soft start method of bidirectional DCDC converter Download PDF

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CN108574404B
CN108574404B CN201710132383.1A CN201710132383A CN108574404B CN 108574404 B CN108574404 B CN 108574404B CN 201710132383 A CN201710132383 A CN 201710132383A CN 108574404 B CN108574404 B CN 108574404B
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dcdc converter
current
duty ratio
synchronous rectification
voltage
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CN108574404A (en
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黄昊
孙政臣
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United Automotive Electronic Systems Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention provides a duty ratio control circuit and a soft start method of a bidirectional DCDC converter, wherein the duty ratio control circuit comprises a voltage single ring, a current single ring, a minimum current ring, a minimum value taking module and a maximum value taking module.

Description

Duty ratio control circuit and soft start method of bidirectional DCDC converter
Technical Field
The invention relates to the technical field of electricity, in particular to a duty ratio control circuit and a soft start method of a bidirectional DCDC converter.
Background
DCDC refers to a direct current switching power supply (also called DC-DC) that can be used for voltage boosting and voltage dropping. DCDC refers to the operation of high-frequency switching through a controllable switch (such as MOSFET) by using the energy storage characteristics of a capacitor and an inductor, so as to store the input electric energy in the capacitor (or the inductor), and when the switch is turned off, the electric energy is released to a load to provide energy. The capability of the DCDC output to be power or voltage is related to the duty cycle (the ratio of the switch on time to the period of the entire switch).
There are two types of DCDC products commonly used in the prior art, one is a Charge Pump (Charge Pump), and the other is an inductive energy storage DCDC converter.
The bidirectional synchronous rectification DCDC converter topology is a topology structure commonly used in the industry and new energy vehicles. The 48V light mixing system of the new energy automobile is widely applied at present, has the characteristics of simple modification and low cost, and is an important factor for attracting various whole automobile factories to start to arrange the automobile types. In a 48V light mixing system, a DCDC converter is used as an important energy conversion part, and direct current electric energy conversion of a 48V side and a 12V side in a vehicle can be realized based on a bidirectional synchronous rectification DCDC converter topology. When a vehicle is just started, the electric energy of a battery at the 12V side is converted to the 48V side through a Boost mode, a capacitor on a motor controller is charged, and the function of pre-charging is completed. In the running process of the vehicle, the battery energy at the 48V side is converted to the load at the 12V side for use mainly by means of a Buck mode, and the battery energy at the 12V side is also converted to the battery energy at the 48V side for use by means of a Boost mode under special working conditions; therefore, the DCDC converter is an indispensable component in the whole system, and the performance of the DCDC converter directly affects the response of the system.
The 48V DCDC converter topology belongs to a parallel synchronous rectification Buck/Boost topology, and the common control mode enables upper and lower half-bridge tubes to be complementary; however, since both ends of the on-vehicle DCDC are connected to the battery, the output characteristics thereof are different according to the load condition. As shown in fig. 1a, under light load, Boost characteristic is also shown in Buck-required mode, that is, reverse current occurs in the same switching period. Due to the coexistence characteristic of Buck and Boost in the same switching period, strong reverse behavior can occur in the soft start process under both Buck and Boost topologies, reverse overcurrent protection is triggered, and the phenomenon of soft start failure is caused; on the other hand, under some special conditions (for example, the output voltage command received by the DCDC converter is lower than the output battery voltage, or the input battery voltage suddenly loses power), the problem of reverse overcurrent fault can be caused.
Disclosure of Invention
The invention aims to provide a duty ratio control circuit and a soft start method of a bidirectional DCDC converter, so as to solve the problem of soft start failure or reverse current fault of the DCDC converter.
In order to solve the above technical problem, the present invention provides a duty cycle control circuit for controlling a duty cycle of a bidirectional synchronous rectification DCDC converter, the duty cycle control circuit comprising:
a voltage single loop for generating a voltage duty cycle based on a reference voltage and an output terminal voltage of the bidirectional synchronous rectification DCDC converter;
a current single loop for generating a current duty cycle based on a reference current and an output terminal current of the bidirectional synchronous rectification DCDC converter;
a minimum current loop for generating a minimum current duty ratio based on a preset minimum current and an output end current of the bidirectional synchronous rectification DCDC converter;
a minimum value taking module for receiving the voltage duty ratio and the current duty ratio, taking the minimum value of the voltage duty ratio and the current duty ratio and outputting the minimum value;
and the maximum value taking module is used for receiving the result output by the minimum value taking module and the minimum current duty ratio, taking the maximum value of the result output by the minimum value taking module and the minimum current duty ratio and outputting the maximum value as the duty ratio of the bidirectional synchronous rectification DCDC converter.
Optionally, in the duty cycle control circuit, the voltage single loop includes:
the first subtracter is used for subtracting the reference voltage and the output end voltage of the bidirectional synchronous rectification DCDC converter;
and the first PID module is used for receiving the result output by the first subtracter and generating a voltage duty ratio according to the result output by the first subtracter.
Optionally, in the duty cycle control circuit, the current single loop includes:
the second subtracter is used for subtracting the reference current and the output end current of the bidirectional synchronous rectification DCDC converter;
and the second PID module is used for receiving the result output by the second subtracter and generating a current duty ratio according to the result output by the second subtracter.
Optionally, in the duty cycle control circuit, the minimum current loop includes:
the third subtracter is used for carrying out subtraction processing on the preset minimum current and the output end current of the bidirectional synchronous rectification DCDC converter;
and the third PID module is used for receiving the result output by the third subtracter and generating the minimum current duty ratio according to the result output by the third subtracter.
Optionally, in the duty cycle control circuit, the first PID module, the second PID module, and the third PID module all use an incremental PID algorithm.
Optionally, in the duty cycle control circuit, the preset minimum current is 0A.
The invention also provides a soft start method of the bidirectional DCDC converter, which comprises the following steps:
providing a bidirectional DCDC converter;
controlling the duty ratio of the bidirectional synchronous rectification DCDC converter by using the duty ratio control circuit;
determining a working mode of a bidirectional synchronous rectification DCDC converter, calculating a duty ratio of a main pipe of the bidirectional synchronous rectification DCDC converter when the main pipe is balanced at volt seconds according to the working mode, and taking the duty ratio of the main pipe when the main pipe is balanced at volt seconds as an initial duty ratio of a duty ratio control circuit;
and the bidirectional synchronous rectification DCDC converter is in soft start in the working mode.
Optionally, in the soft start method of the bidirectional DCDC converter, the operation mode of the bidirectional DCDC converter is a step-up mode or a step-down mode.
Optionally, in the soft start method of the bidirectional DCDC converter, the topology of the bidirectional DCDC converter includes: the power supply comprises a first direct current power supply, a second direct current power supply, a first MOS switch, a second MOS switch, an inductor and a capacitor; the first direct-current power supply, the inductor and the second direct-current power supply are sequentially connected in series, the capacitor is connected to two ends of the second direct-current power supply in parallel, the first MOS switch is arranged between the anode of the first direct-current power supply and the inductor, and the second MOS switch is arranged between the cathode of the first direct-current power supply and the inductor;
when the working mode of the bidirectional synchronous rectification DCDC converter is determined to be a voltage reduction mode, the initial duty ratio of the duty ratio control circuit is equal to the ratio of the voltage at the output end of the bidirectional synchronous rectification DCDC converter to the voltage at the input end of the bidirectional synchronous rectification DCDC converter;
when the working mode of the bidirectional synchronous rectification DCDC converter is determined to be the boosting mode, the initial duty ratio of the duty ratio control circuit is equal to 1 minus the ratio of the voltage at the input end of the bidirectional synchronous rectification DCDC converter to the voltage at the output end of the bidirectional synchronous rectification DCDC converter.
In the duty ratio control circuit and the soft start method of the bidirectional DCDC converter provided by the invention, the duty ratio control circuit comprises a voltage single ring, a current single ring, a minimum current ring, a minimum value taking module and a maximum value taking module; the minimum value module receives a voltage Duty ratio generated by a voltage single ring and a current Duty ratio generated by a current single ring, the voltage Duty ratio and the current Duty ratio are minimum and output to the maximum value module, and the maximum value module takes the maximum value of the result output by the minimum value module and the minimum current Duty ratio Duty4MinCur generated by the minimum current ring and outputs the result as the Duty ratio of the bidirectional synchronous rectification DCDC converter. Compared with the existing duty ratio control circuit, the minimum current loop and the maximum value taking module are additionally arranged, when the output voltage instruction of the DCDC converter is low, the pump power is supplied or the input voltage of the DCDC converter is in power failure, the minimum current loop duty ratio generated by the minimum current loop replaces the result output by the minimum value taking module, the duty ratio is effectively prevented from further decreasing, the DCDC converter is maintained to output in the forward direction with the preset minimum current, and the reverse overcurrent fault is effectively avoided.
Drawings
FIG. 1a is a schematic diagram of the operating state of a conventional soft start, bi-directional DCDC converter;
FIG. 1b is a waveform diagram of the inductor current in the initial stage of a conventional soft start;
FIG. 2 is a schematic structural diagram of a duty cycle control circuit according to a first embodiment of the present invention;
fig. 3 is a flowchart of a soft start method of a bidirectional synchronous rectification DCDC converter according to a second embodiment of the present invention;
fig. 4 is a schematic diagram of a topology of a bidirectional synchronous rectification DCDC converter in the first or second embodiment of the present invention.
In fig. 2: voltage single ring-1; a first subtractor-10; a first PID module-11; current single ring-2; a second subtractor-20; a second PID module-21; minimum current loop-3; a third subtractor-30; a third PID module-31; taking a minimum value module-4; maximum value module-5;
in fig. 4: a first direct current power supply-6; a second DC power supply-7; a first MOS switch-100; a second MOS switch-101; an inductor-8; and a capacitor-9.
Detailed Description
The duty cycle control circuit and the soft start method of the bidirectional DCDC converter according to the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
< example one >
Referring to fig. 2, it is a schematic structural diagram of a duty cycle control circuit, as shown in fig. 2, the duty cycle control circuit includes: the bidirectional synchronous rectification DCDC converter comprises a voltage single ring 1, a current single ring 2, a minimum current ring 3, a minimum value taking module 4 and a maximum value taking module 5, wherein the voltage single ring 1 is used for generating a voltage Duty ratio Duty4Vtg based on a reference voltage Vref and an output end voltage Vo of the bidirectional synchronous rectification DCDC converter; the current single ring 2 is used for generating a current Duty ratio Duty4Cur based on a reference current Iref and an output end current Io of the bidirectional synchronous rectification DCDC converter; the minimum current loop 3 is used for generating a minimum current Duty ratio Duty4MinCur based on a preset minimum current Imin and the output end current Io of the bidirectional synchronous rectification DCDC converter; the minimum value taking module 4 is configured to receive the voltage Duty cycle and the current Duty cycle Duty4Cur, take a minimum value for the voltage Duty cycle and the current Duty cycle Duty4Cur, and output the minimum value; the maximum value taking module 5 is configured to receive the result output by the minimum value taking module 4 and the minimum current Duty ratio Duty4MinCur, take a maximum value (the result is Duty4Final in fig. 2) for the result output by the minimum value taking module 4 and the minimum current Duty ratio Duty4MinCur, and output the maximum value as the Duty ratio of the bidirectional synchronous rectification DCDC converter. The value of the preset minimum current Imin is set according to a requirement, and is set to 0A in this embodiment.
The normal DCDC converter uses the result output by the minimum value module 4 as the duty ratio, so when the voltage command is lower than the output-side battery voltage (or pump the output-side battery), the duty ratio will finally decrease to 0, and according to the analysis of fig. 1a, the reverse overcurrent protection will be triggered. In addition, when the input voltage is in power failure, the duty ratio is not adjusted in time, the area of the Buck triangle is quickly reduced to be smaller than that of the Boost triangle, and a reverse overcurrent fault is caused. Due to the existence of the minimum current loop 3, when the output voltage instruction of the DCDC converter is low, the pump power is supplied or the input voltage of the DCDC converter is powered off, the minimum current loop Duty ratio Duty4MinCur generated by the minimum current loop 3 replaces the result output by the minimum value taking module 4, and the Duty ratio is effectively prevented from further decreasing, so that the DCDC converter is maintained to output in the forward direction by the preset minimum current Imin, and the reverse overcurrent fault is effectively avoided.
With continued reference to fig. 2, the voltage single loop 1 includes: a first subtractor 10 and a first PID module 11; the first subtractor 10 is configured to subtract the reference voltage Vref and the output terminal voltage Vo of the bidirectional synchronous rectification DCDC converter; the first PID module 11 is configured to receive the result Err1 output by the first subtractor 10, and generate a voltage Duty ratio Duty4Vtg according to the result Err1 output by the first subtractor 10.
The current single loop 2 includes: a second subtractor 20 and a second PID module 21; the second subtractor 20 is configured to subtract the reference current Iref and the output end current Io of the bidirectional synchronous rectification DCDC converter; the second PID module 21 is configured to receive the result Err2 output by the second subtractor 20, and generate a current Duty cycle Duty4Cur according to the result Err2 output by the second subtractor 20.
The minimum current loop 3 includes: a third subtractor 30 and a third PID module 31; the third subtractor 30 is configured to subtract a preset minimum current Imin from an output current Io of the bidirectional synchronous rectification DCDC converter; the third PID module 31 is configured to receive the result Err3 output by the third subtractor 30, and generate a minimum current Duty ratio Duty4MinCur according to the result Err3 output by the third subtractor 30.
Preferably, the first PID module 11, the second PID module 21 and the third PID module 31 all use an incremental PID algorithm.
< example two >
The embodiment provides a soft start method of a bidirectional synchronous rectification DCDC converter. A duty ratio is mainly calculated according to the working state of the bidirectional synchronous rectification DCDC converter and is used as the initial duty ratio of the bidirectional synchronous rectification DCDC converter, so that the reverse mode of the bidirectional synchronous rectification DCDC converter in the same switching period in the soft start process is restrained, reverse current is avoided, and normal soft start of the bidirectional synchronous rectification DCDC converter is ensured.
Specifically, please refer to fig. 3 and fig. 4 for understanding:
first, step S1 is executed: providing a bidirectional synchronous rectification DCDC converter;
next, step S2 is executed: controlling the duty ratio of the bidirectional synchronous rectification DCDC converter by using a duty ratio control circuit in the first embodiment;
next, step S3 is executed: determining a working mode of a bidirectional synchronous rectification DCDC converter, calculating a duty ratio of a main pipe of the bidirectional synchronous rectification DCDC converter when the main pipe is balanced at volt seconds according to the working mode, and taking the duty ratio of the main pipe when the main pipe is balanced at volt seconds as an initial duty ratio of a duty ratio control circuit; the operating mode of the bidirectional DCDC converter is a Boost mode (also called Boost mode) or a Buck mode (Buck mode).
Next, step S4 is executed: and the bidirectional synchronous rectification DCDC converter is in soft start in the working mode. At the time of soft start, the duty ratio of the bidirectional synchronous rectification DCDC converter starts from the initial duty ratio instead of 0.
The method of the embodiment can inhibit the reverse mode of the bidirectional synchronous rectification DCDC converter in the same switching period in the soft start process, avoid the occurrence of reverse current, and ensure the normal soft start principle of the bidirectional synchronous rectification DCDC converter as follows:
referring to fig. 1a and fig. 4, taking the Buck mode (also called Buck mode) as an example, as shown in fig. 1a, in a working cycle, if the area of a triangle below the horizontal axis is larger than the area of a triangle above the horizontal axis, the overall behavior is Boost behavior, otherwise, Buck behavior is exhibited. If the Boost action is too strong, a large reverse current can be generated, and overcurrent protection is triggered under severe conditions. To suppress reverse current, it is common practice to turn off the synchronous rectifier (for Buck, the down tube, i.e., the second MOS switch); for this reason, it is necessary to design an independent half-bridge up-down tube drive, which means an isolated drive power supply, and this results in high product cost. From the perspective of reducing cost, the bootstrap driver chip is better to use, but the driving power supply of the upper tube depends on the charging of the bootstrap capacitor when the lower tube is turned on, and the lower tube is guaranteed to be turned on in each switching period, which brings difficulty to the suppression of reverse current.
In a conventional soft start mode, duty ratio outputs of a main pipe (an upper pipe for Buck) of a topology are gradually accumulated from 0 to the top, and as can be seen from fig. 1a, the smaller the duty ratio is, the weaker the Buck behavior is, and the stronger the Boost behavior is. In the initial stage of soft start, the Boost behavior is strongest, and the Boost behavior is gradually weakened along with the increase of the duty ratio of the main pipe. In the initial stage of soft start, the inductor current waveform is shown in fig. 1b, and it can be seen that the reverse current becomes larger.
Therefore, the key to the success of soft start is to suppress the early reverse inductor 8 current.
Taking the topology of the bidirectional synchronous rectification DCDC converter as an example of the structure shown in fig. 4, the topology of the bidirectional synchronous rectification DCDC converter includes: a first direct current power supply 6, a second direct current power supply 7, a first MOS switch 100, a second MOS switch 101, an inductor 8 and a capacitor 9; first direct current power supply 6, inductance 8, second direct current power supply 7 establish ties in proper order, electric capacity 9 connect in parallel in the both ends of second direct current power supply 7, first MOS switch 100 set up in first direct current power supply 6 the positive pole with between the inductance 8, second MOS switch 101 set up in first direct current power supply 6 the negative pole with between the inductance 8.
Taking Buck as an example, the main tube (i.e. the upper tube, the first MOS switch) is in the conducting stage,
Figure BDA0001240418090000081
a main pipe shut-down stage, wherein,
Figure BDA0001240418090000082
to suppress reverse current, the switching period is guaranteedThe average inductor 8 current is not less than 0, namely the Buck triangle area in FIG. 4 is ensured to be larger than the Boost triangle area. Let the current of inductor 8 rise to i in one switching cycleincrThe value of the drop is idecrThen there are:
Figure BDA0001240418090000083
Figure BDA0001240418090000084
iincr＝idecrthe duty cycle of this critical state is
Figure BDA0001240418090000085
Wherein D isinitRepresents the duty cycle of the critical state, D represents the steady-state duty cycle, Vout represents the output voltage, Vin represents the input voltage, and Ts represents the switching period.
Similarly, the duty ratio of the critical state in Boost mode can be derived as
Figure BDA0001240418090000086
Since the duty cycle is getting larger and larger during soft start, the initial duty cycle can be set to D in the complementary mode accordinglyinit。
The topology of the bidirectional synchronous rectification DCDC converter includes, but is not limited to, the topology shown in fig. 4, and other topologies may be used as long as the duty ratio that is mainly in the critical state at the volt-second balance is used as the initial duty ratio of the soft start of the DCDC converter according to the topology and the above calculation principle.
The initial duty cycle is selected as DinitThe average value of the inductor current will always be kept positive and the system can be normally soft started.
In the soft starting process, in order to ensure that the duty ratio in the soft starting process of the bidirectional synchronous rectification DCDC converter is from the initial duty ratio DinitBegin to increase slowly, requireA step PID, i.e., a slow increase in voltage command, is used for soft start.
The duty ratio is calculated by adopting a stepping PID, and iterative calculation is carried out by adopting a mode shown as the following formula:
Err(n)＝Ref_temp-Out(n)；
Duty(n)＝Duty(n-1)+Kp*[Err(n)-Err(n-1)]+Ki*Err(n)+Kd*[Err(n-2)+Err(n)-2*Err(n-1)]；
Err(n-2)＝Err(n-1)；
Err(n-1)＝Err(n)；
Duty(n-1)＝Duty(n)；
Duty(0)＝Dinit。
err (n) represents a difference between the reference value and the output value after the current operation, Ref _ temp represents the reference value, out (n) represents the output value after the current operation, duty (n) represents the duty ratio after the current operation, n represents the current operation, Kp represents a proportional coefficient, Ki represents an integral coefficient, and Kd represents a differential coefficient.
Referring to fig. 2, Err1, Err2, and Err3 in fig. 2 should be represented as Err1(n), Err2(n), and Err3(n) in the incremental PID, and because the PID expression is not only incremental, Err1(n), Err2(n), and Err3(n) are not used in fig. 2.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
In summary, in the duty cycle control circuit and the soft start method of the bidirectional DCDC converter provided by the present invention, the duty cycle control circuit includes a voltage single loop, a current single loop, a minimum current loop, a minimum value module, and a maximum value module; the minimum value module receives a voltage duty ratio generated by a voltage single ring and a current duty ratio generated by a current single ring, the minimum value of the voltage duty ratio and the current duty ratio is obtained and output to the maximum value obtaining module, and the maximum value module obtains the maximum value of the result output by the minimum value obtaining module and the minimum current duty ratio generated by the minimum current ring and outputs the result as the duty ratio of the bidirectional synchronous rectification DCDC converter. Compared with the existing duty ratio control circuit, the minimum current loop and the maximum value taking module are additionally arranged, when the output voltage instruction of the DCDC converter is low, the pump power is supplied or the input voltage of the DCDC converter is in power failure, the minimum current loop duty ratio generated by the minimum current loop replaces the result output by the minimum value taking module, the duty ratio is effectively prevented from further decreasing, the DCDC converter is maintained to output in the forward direction with the preset minimum current, and the reverse overcurrent fault is effectively avoided.
The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.

Claims (9)

1. A duty cycle control circuit for controlling a duty cycle of a bi-directional synchronous rectified DCDC converter, comprising:
a voltage single loop for generating a voltage duty cycle based on a reference voltage and an output terminal voltage of the bidirectional synchronous rectification DCDC converter;
a current single loop for generating a current duty cycle based on a reference current and an output terminal current of the bidirectional synchronous rectification DCDC converter;
a minimum current loop for generating a minimum current duty ratio based on a preset minimum current and an output end current of the bidirectional synchronous rectification DCDC converter;
a minimum value taking module for receiving the voltage duty ratio and the current duty ratio, taking the minimum value of the voltage duty ratio and the current duty ratio and outputting the minimum value;
and the maximum value taking module is used for receiving the result output by the minimum value taking module and the minimum current duty ratio, taking the maximum value of the result output by the minimum value taking module and the minimum current duty ratio and outputting the maximum value as the duty ratio of the bidirectional synchronous rectification DCDC converter.
2. The duty cycle control circuit of claim 1, wherein the voltage single loop comprises:
the first subtracter is used for subtracting the reference voltage and the output end voltage of the bidirectional synchronous rectification DCDC converter;
and the first PID module is used for receiving the result output by the first subtracter and generating a voltage duty ratio according to the result output by the first subtracter.
3. The duty cycle control circuit of claim 2, wherein the current single loop comprises:
the second subtracter is used for subtracting the reference current and the output end current of the bidirectional synchronous rectification DCDC converter;
and the second PID module is used for receiving the result output by the second subtracter and generating a current duty ratio according to the result output by the second subtracter.
4. The duty cycle control circuit of claim 3, wherein the minimum current loop comprises:
the third subtracter is used for carrying out subtraction processing on the preset minimum current and the output end current of the bidirectional synchronous rectification DCDC converter;
and the third PID module is used for receiving the result output by the third subtracter and generating the minimum current duty ratio according to the result output by the third subtracter.
5. The duty cycle control circuit of claim 4, wherein the first PID module, the second PID module, and the third PID module each employ an incremental PID algorithm.
6. The duty cycle control circuit of any one of claims 1-5, wherein the preset minimum current is 0A.
7. A soft start method of a bidirectional synchronous rectification DCDC converter is characterized by comprising the following steps:
providing a bidirectional synchronous rectification DCDC converter;
controlling the duty cycle of the bi-directional synchronous rectified DCDC converter using the duty cycle control circuit of any of claims 1-6;
determining a working mode of a bidirectional synchronous rectification DCDC converter, calculating a duty ratio of a main pipe of the bidirectional synchronous rectification DCDC converter when the main pipe is balanced at volt seconds according to the working mode, and taking the duty ratio of the main pipe when the main pipe is balanced at volt seconds as an initial duty ratio of a duty ratio control circuit;
the bidirectional synchronous rectification DCDC converter is in soft start in the working mode;
wherein: the working modes of the bidirectional synchronous rectification DCDC converter comprise a Buck mode and a Boost mode, when the working mode is the Buck mode, the main pipe is an upper pipe, and when the working mode is the Boost mode, the main pipe is a lower pipe.
8. The soft-start method of the bi-directional synchronous rectification DCDC converter as claimed in claim 7, wherein the operation mode of the bi-directional synchronous rectification DCDC converter is a step-up mode or a step-down mode.
9. The soft-start method of a bi-directional synchronous rectified DCDC converter of claim 7, wherein the topology of the bi-directional synchronous rectified DCDC converter comprises: the power supply comprises a first direct current power supply, a second direct current power supply, a first MOS switch, a second MOS switch, an inductor and a capacitor; the first direct-current power supply, the inductor and the second direct-current power supply are sequentially connected in series, the capacitor is connected to two ends of the second direct-current power supply in parallel, the first MOS switch is arranged between the anode of the first direct-current power supply and the inductor, and the second MOS switch is arranged between the cathode of the first direct-current power supply and the inductor;
when the working mode of the bidirectional synchronous rectification DCDC converter is determined to be a voltage reduction mode, the initial duty ratio of the duty ratio control circuit is equal to the ratio of the voltage at the output end of the bidirectional synchronous rectification DCDC converter to the voltage at the input end of the bidirectional synchronous rectification DCDC converter;
when the working mode of the bidirectional synchronous rectification DCDC converter is determined to be the boosting mode, the initial duty ratio of the duty ratio control circuit is equal to 1 minus the ratio of the voltage at the input end of the bidirectional synchronous rectification DCDC converter to the voltage at the output end of the bidirectional synchronous rectification DCDC converter.
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